The present invention relates to a process for the stabilisation of particles containing peroxygen compounds by coating using coating agents that are insoluble in water and melt at low temperatures such as waxes and bleaching compositions containing particles stabilised according to this process.
It is well-known to use certain peroxygen compounds in the form of particles as bleaching agents in detergent powder mixtures. In conventional household detergent compositions, particles of sodium perborate tetrahydrate are habitually tested as a bleaching compound because they are relatively stable towards decomposition in a detergent powder medium. It is becoming increasingly common, however, to use cold methods of washing and soaking clothes for which sodium perborate has the disadvantage of dissolving too slowly. In order to overcome this disadvantage, it has been suggested that particles of other inorganic peroxygen compounds be introduced into detergent powders notably alkali metal percarbonates, perphosphates and peroxymonosulphates, which have suitable rates of dissolution at low temperatures. These peroxygen compounds and particularly the percarbonates decompose too radpily in the powder state, particularly when they are stored in a moist atmosphere. Moreover, the other constituents of detergent compositions often initiate this decomposition.
Numerous processes have been put forward to overcome these disadvantages and to improve the stability of particles of peroxygen compounds such as percarbonates. It was thus suggested in U.S. Pat. No. 3,847,830 filed on Jan. 17, 1972 and assigned to Laporte Industries Limited that they be coated with coating agents that are insoluble in water and melt at low temperatures, based on fatty acids alkanolamides of fatty acids, glycerol esters of fatty acids, long-chain alcohols or paraffin waxes. The methods used to effect coating are complicated because of the fact that the coating agent is insoluble in water. They require the dissolution of the coating agent in an organic solvent or its use in the melted form. This first technique involves the elimination of great amounts of solvent which render the process complex, while in the second, the quantities of coating agent required to achieve sufficient stability of the particles of peroxygen compounds are relatively large, the effect of which is to reduce the active oxygen content of the stabilised particles obtained and to reduce unduly the rate of dissolution in water of the peroxygen compound.